Isotopic paleodiet analysis at 2nd c AD Rogowo, PL
Laurie J. Reitsema and Tomasz Kozłowski
Anthropological Review • Vol. 76 (1), 1–22 (2013)
Diet and society in Poland before the state:
stable isotope evidence from a Wielbark
population (2nd c. AD)
Laurie J. Reitsema1, Tomasz Kozłowski2
Department of Anthropology, University of Georgia, 250 Baldwin Hall, Jackson St., Athens,
Georgia, 30602, USA
2
Department of Anthropology, Nicolaus Copernicus University, ul. Lwowska 1, 87-100,
Toruń, Poland
1
Abstract: The 1st–4th c. AD Wielbark culture of Eastern Europe is relatively understudied bioarchaeologically due to the fragmentary nature of its cemeteries. Here, we report the first stable isotope analysis of
Wielbark diet using stable carbon and nitrogen isotope signatures from both collagen and carbonate of 30
individuals from Rogowo, a 2nd c. Wielbark cemetery in North-Central Poland. Diet at Rogowo was primarily based on terrestrial foods and included millet, a C4 plant cultivated by many Slavic populations in
Europe. Anadromous fish likely supplemented the diet, which is clarified when considering collagen and
carbonate data in tandem. Stable isotope differences between the sexes indicate that men and women may
have consumed different foods, although there is a possibility that women immigrated to Rogowo from
an isotopically different region of Europe. No significant differences are noted in δ13C or δ15N of women
with and without grave goods, suggesting little social differentiation within the Wielbark culture, at least
in terms of daily food access. Reconstructing human diet in Europe through stable isotope analysis is
problematic because of the relative isotopic homogeneity in this region of the world. This study further
demonstrates the utility of using both carbonate and collagen stable isotope data in tandem to reconstruct
past European diet.
Key words: paleodiet, Roman era, Wielbark culture, isotopes, Poland
Introduction
The archaeological culture known
as the Wielbark occupied regions of
North-Central Europe between the 1st
and 4th centuries AD (Barford 2001).
This time period is referred to as the pe-
riod of Roman influence or the Roman
era by archaeologists, although the geographic regions of modern-day Poland
were never incorporated into the Roman
Empire. Initially settled in the areas surrounding the Vistula River in Pomera-
Original Article: Received September 13, 2013; Accepted for publication October 21, 2013
DOI: 110.2478/anre-2013-0010
© 2013 Polish Anthropological Society
2
Laurie J. Reitsema and Tomasz Kozłowski
nia (Wołgiewicz 1981, Godłowski and
Kozłowski 1985), the Wielbark culture
expanded during the first half of the 2nd
c. AD to Southeast Poland and Wielkopolska (Kozak-Zychman 1996). Origins
of the Wielbark culture are uncertain. It
may have developed indigenously from
the Oksywie culture in and around the
Vistula River basin (e.g., Godłowski
and Kozłowski 1985; Dąbrowski 2006),
but some believe it may represent immigrant populations of Germanic Goths
and Gepids from Scandinavia (Czekanowski 1955; Godłowski and Kozłowski
1985; Heather 1996; Kozak-Zychman
1996; Wołgiewicz 1981). The issue of
Wielbark origins and relationships with
other Roman era European populations
remains unresolved. After their appearance in North-Central Poland, Wielbark
settlements eventually shift further
south, replacing the Przeworsk culture
in Southern Poland, and apparently developing into the Černjachov culture in
modern-day Ukraine and surrounding
areas. The relationship between the
Wielbark culture and later, medieval
Slavic populations from the Oder and
the Vistula rivers basins is also incompletely defined (c.f., Kozak-Zychman
1996; Dąbrowski 2006). Anthropological examinations of skull and tooth morphology suggest biological continuity
between Antiquity and the early medieval period (Piontek et al. 2008). Recent
preliminary aDNA analyses of a small
number of Iron Age and medieval skeletons from Poland suggest genetic discontinuity between these times (Juras
2012). Although inconclusive thus far,
contributions from biological anthropology, such as these recent examples,
are desirable to clarify the Wielbark culture’s relationship to other European
populations.
Two archaeological trademarks of the
Wielbark culture are bi-ritual cemeteries
that include both inhumation and cremation burials, and a characteristic lack of
weapons and tools as grave goods (Godłowski and Kozłowski 1985). ­Wielbark
settlements are generally open and unfortified. A degree of social differentiation is manifest in the facts that some
graves are cremations whereas some
are inhumations, and that ornaments
and jewelry grave goods are present in
burials. However, in general, Wielbark
populations appear to have been relatively egalitarian (Gieysztor et al. 1979).
Although linked to the Roman world by
trade, Slavic populations in Antiquity
are scarcely described in written records;
thus, it falls to archaeology to illuminate
the daily lives of modern-day Poland’s
populations in the early centuries AD.
In terms of the subsistence economy, wheat, millet, rye and barley were
the most commonly grown crops by the
Wielbark culture (Pyrgała 1975). Cattle
were the most common domesticated
animal in Roman era Poland, comprising
approximately 50 to 80% of the total archaeozoological assemblages (Gładykowska-Rzeczycka et al. 1997; Makowiecki
2006; Reitsema et al. 2013). Land was
tilled on a household level but was probably collectively owned during the tribal
period (Gieysztor et al. 1979). For this
reason, little within-group dietary differentiation based on status may be expected at this time.
Because most Wielbark cemeteries
comprise cremains and fragmented skeletal remains, only a limited number of bioarchaeological investigations contribute
to our understanding of these peoples
(e.g., Dąbrowski 2006; Kozak-Zychman
1996, Krenz-Niedbala and Kozłowski
2013; Piontek et al. 2006; Segeda et al.
Isotopic paleodiet analysis at 2nd c AD Rogowo, PL
2007; Smrćka et al. 2000). Here we present the first stable isotope evidence of
Wielbark diet from Rogowo, a cemetery
with unusually complete skeletal materials, in Kujavian-Pomeranian Voivodeship
of North-Central Poland. In addition to
reconstructing diet of this Wielbark population, we consider relationships between diet and sex, age, and presence/
absence of grave goods to better understand the dual influences of cultural and
biological variables in influencing diet of
this tribal population.
Stable Isotope Background
Analysis of stable carbon and nitrogen
isotopes from human bones is an effective tool in archaeology for reconstructing individual diets of past populations
(c.f., Katzenberg 2008; Schoeninger
2011). Plants and animals exhibit systematic isotopic variation due to differences in their environments, physiologies and diets (Ambrose 2000; Park and
Epstein 1961; Schoeninger and Moore
1992; van Klinken et al. 2000). Stable
isotope signatures are incorporated
into consumer tissues, including bones,
which come to represent a composite of
the stable isotope signatures of foods
eaten in life. By measuring stable isotope ratios of ancient bones and comparing the signatures to known ratios
of various food types, it is possible to
estimate the types of foods a person typically consumed on a daily basis. Stable
isotope values are expressed as a permil
(‰) ratio of one of an element’s isotopes to another in relation to a standard of known abundance: Vienna Pee
Dee Belemnite (VPDB) for δ13C and the
Ambient Inhalable Reservoir (AIR) for
δ15N. Both stable carbon isotope ratios
(δ13C) and stable nitrogen isotope ra-
3
tios (δ15N) are reported according to the
equation
[δ=(Rsample – Rstandard)/Rstandard x1000].
Stable carbon and nitrogen isotope
ratios provide differing information
about human diet. δ13C variation in the
plant kingdom exists due to differences
in photosynthetic pathways used to metabolize atmospheric carbon (Park and
Epstein 1960; Smith and Epstein 1971).
δ13C ratios in human tissues therefore
reflect the local ecosystem, identifying
which types of plants were consumed
and the influence of environmental parameters on plant δ13C values (DeNiro
and ­Epstein 1978; Heaton 1999). The
δ13C values of fish often (though not always) fall outside the typical ranges of
terrestrial foods, and can in many cases
be identified isotopically in diet as a result (Chisholm et al. 1982; Dufour et al.
1999; Grupe et al. 1999; Schoeninger and
DeNiro 1984).
Stable carbon isotope ratios can be
measured from either bone collagen or
apatite (referred to henceforth as δ13Ccoll
and δ13Cap, respectively). Because collagen
is formed from amino acids, it primarily reflects protein in the diet (­Ambrose
and Norr 1993; Tieszen and Fagre 1993).
Apa­tite is formed from dissolved bicarbonate in the bloodstream which contains
carbon from all macronutrients; thus,
carbonate from apatite better reflects energy sources in diet (i.e., carbohydrates).
Collagen and carbonate provide different
and complementary information about
foods consumed and when used together, have been shown to be highly effective for reconstructing diet (e.g., Kellner
and Schoeninger 2007).
The δ13C values of consumers are not
identical to the values of foods. Rather,
there are systematic diet-tissue spacing
relationships that can be considered in
4
Laurie J. Reitsema and Tomasz Kozłowski
order to backtrack from the stable isotope ratios of a consumer to those of
its foods. In general, collagen δ13Ccoll is
approximately 5‰ higher in consumers than in the bulk protein diet (van
der Merwe and Vogel 1978). The relationship between δ13Cap and diet is less
well-established. Controlled laboratory
experiments reveal the diet-to-apatite
space for δ13C to be approximately 9.5‰
among small mammals (Ambrose and
Norr 1993; Tieszen and Fagre 1993), but
a review by Garvie-Lok (2001) of published studies suggests a larger value of
approximately 12.0‰ may be more appropriate for humans.
Stable nitrogen isotopes reflect the
trophic level of a consumer, with carnivores systematically exhibiting higher
δ15N signatures than herbivores due to
physiological and chemical processes
during metabolism (DeNiro and Epstein
1981). The diet-tissue space for δ15N is
generally on the order of 3–5‰ (­Drucker
and Bocherens 2004). δ15N values in collagen can thus be used to estimate the
amounts and types of animal products
consumed, with higher values in consumers suggesting greater animal protein intake. However, δ15N values also vary with
respect to local climate (Ambrose 1991;
Drucker et al. 2003), soil nitrogen composition (Britton et al. 2008; Grogan et
al. 2000), production systems (Bogaard
et al. 2007; Commisso and Nelson 2008)
and consumer physiology (Ambrose
1991; Fuller et al. 2005; ­Hobson et al.
1993), complicating their interpretation.
Isotopic evidence from animal bones in
this region of Poland dating to the medieval period shows a 3.3‰ difference in
δ15N values and a 1.4‰ difference in δ13C
values of wild and domestic animals (Reitsema et al. 2013). Higher δ15N values
among domestic animals likely reflects
the use of manure or other methods used
to improve soils (ploughing; burning) on
which domestic animals were grazed. For
δ13C, the wild/domestic animal difference
likely represents variations in canopy
cover on forage lands, with forest plants
and animals exhibiting lower values due
to the “canopy effect” (for more information on the canopy effect in Europe, see
Bocherens and Drucker (2003)).
The value of stable isotope analysis in
historic archaeology is that, unlike written records, stable isotope signatures
are unaffected by record biases in the
prevailing sociopolitical milieu, making
them more direct indicators of an individual’s diet. Historical documentation
of the Roman era in Northern Europe
is limited by the fact that most inhabitants and travelers were illiterate, leaving many populations fragmentarily or
subjectively represented in records. Interpretations of archaeolozoological and
paeobotanical data are limited in that
they represent a bulk average of overall
diet among the entire population, rather than differential food access among
sub-populations. Stable isotope analysis
has proven invaluable in anthropology
not just for understanding subsistence
behaviors, but also for recognizing sex-,
age- and status-based differences in food
access (Katzenberg 1993; Larsen 1997;
Polet and Katzenberg 2003; Privat et al.
2002; Reitsema et al. 2010; Reitsema and
Vercellotti 2012).
Materials and Methods
Rogowo is a Roman era cemetery discovered in 1984 that dates to the 2nd c. AD
(Fig. 1). It was excavated in 1999 and
2000, and is associated with a nearby settlement that covers approximately 6 ha
(Krenz-Niedbała and Kozłowski 2013).
Isotopic paleodiet analysis at 2nd c AD Rogowo, PL
The cemetery includes 137 inhumation
and 151 cremation burials (Chudziak
2000). Skeletons were interred in a flexed
position, many with copper-alloy jewelry
that has left green stains on skeletal elements (Fig. 2). One of Eastern Europe’s
most important trade routes, the Amber
Road, connected Rogowo with the Baltic
Sea to the North, and the Roman Empire
to the South (Buko 2008). Interregional
trade and iron smelting, in addition to
animal husbandry and agriculture, structured the economy of this Wielbark population (Piontek et al. 2006).
From the cemetery, small pieces of rib
approximately 1–2 cm in length from 15
adult males and 15 adult females were
Fig. 1. Map of Poland showing the location of Rogowo (geographic coordinates: 53° 4′ 41″ N,
18° 44′ 18″ E)
Fig. 2. Burial 59 from Rogowo, referred to as a
“princess” on account of her rich jewelry. Photographed by Adam Szwarc
5
sampled. No animal bones were found
at the site, and so an interpretive faunal
baseline was established using animals
from Denmark which were contemporaneous with Rogowo, previously reported
by Jørkov et al. (2010), and animals from
medieval Poland, reported here and in
more detail by Reitsema et al. (2013).
Collagen was purified from bone using a modified Longin method (Ambrose 1990; Ambrose et al. 1997). Briefly,
approximately 0.25–0.50 g of bone was
crushed to a coarse powder, demineralized for 3 to 7 days in 0.2 M HCl, soaked
in 0.125 M NaOH for 20 hours to remove
other contaminants, solubilized at 90ºC
in HCl of pH=3, filtered and freeze dried.
Three human samples were analyzed in
duplicate, and one sample was both prepared and analyzed in duplicate. These
repeat analyses show replicability to be
within 0.1‰ for δ15N and 0.2‰ for δ13C.
Of the 30 human samples analyzed
for collagen isotope data, 29 were also
analyzed for carbonate data. Carbonate
was prepared according to protocol detailed in Garvie-Lok et al. (2004). Bone
was powdered in a steel mortar and pestle, deproteinated in bleach for 48 hours,
soaked in 0.1 M acetic acid for 4 hours
to remove more soluble adsorbed carbonates, dried, and homogenized in an
agate mortar and pestle. Two samples
were run in duplicate. The mineral composition of all 29 apatite samples was examined using Fourier transform infrared
spectroscopy (FTIR) to check for diagenesis, a technique described in greater detail by Wright and Schwarcz (1996). The
two FTIR measurements used to evaluate preservation of carbonate are crystallinity index (CI), and carbonate content
as estimated by a carbonate-phosphate
ratio (C/P). We also consider peaks or
shoulders at wavelength 1096 cm–1, in-
6
Laurie J. Reitsema and Tomasz Kozłowski
dicative of recrystallization to francolite, as a window into post-mortem alteration of bone (Wright and Schwarcz
1996). CI and C/P values far outside the
range of modern bone suggest either
that contaminating substances are present in the sample, or that the sample has
recrystallized during deposition or sample preparation, both of which may shift
the isotope signatures in carbonate away
from biogenic values (Berna et al. 2004;
Nagy et al. 2008; Szostek 2009; Szostek
et al. 2011; Yoder and Bartelink 2010).
We also examine the stable oxygen isotope ratios (δ18O) of all apatite samples
as a complementary proxy indicator of
diagenetic alteration, after Wright and
Schwarcz (1996) and Garvie-Lok (2001).
The rationale behind using δ18O values
as indicators of diagenesis rather than as
biogenic paleodiet indicators is that δ18O
values in bone apatite are more affected than δ13C values by fractionation that
occurs during changes between different
species of carbonate in bone during sample treatment or diagenesis (Wright and
Schwarcz 1996). Whereas the ranges
of FTIR values alone do not necessarily
indicate diagenesis per se (considerable
scatter has been documented in both
modern and “well-preserved” archaeological bone; see for example Wright
and Schwarcz [1996] and Garvie-Lok et
al. [2004]), correlations between δ18O
and FTIR values cannot parsimoniously be explained otherwise (Wright and
Schwarcz 1996; Garvie-Lok 2001). Animal bones from medieval Poland were
prepared in the same manner as human
bones (for more details on the animal
bones used in this study, see Reitsema
et al. 2013).
All stable isotope analyses were conducted in the Stable Isotope Biogeochemistry Laboratory at the Ohio State Uni-
versity. Collagen samples were analyzed
on a Costech Elemental Analyzer coupled to a Finnigan Delta IV Plus stable
isotope ratio mass spectrometer under
continuous flow using a CONFLO III interface. Stable carbon and nitrogen measurements were made where the average
standard deviation of repeated measurements of the USGS24 and IAEA-N1
standards were between 0.04‰ and
0.07‰ for δ13Ccoll and between 0.07‰
and 0.18‰ for δ15N. We report δ13Ccoll
values to the nearest 0.1‰.
For carbonate, a 1.0–1.2 mg subsample was analyzed for δ13Cap relative
to the Vienna Peedee Belemnite Limestone standard using an automated Carbonate Kiel device coupled to the mass
spectrometer. Samples were acidified
under vacuum with 100% ortho-phosphoric acid, the resulting CO2 cryogenically purified, and delivered to the mass
spectrometer. Three samples were run
in duplicate and replicability was within
0.20‰ for δ13C. The standard deviation
of repeated measurements of limestone
internal standard (NBS-19) for δ13Cap
was ± 0.03‰. Because of high precision
for carbonate measurements, we report
δ13Cap values to the nearest 0.01‰.
Results
The preservation quality of collagen
samples was assessed using C:N ratios,
%C and %N following criteria outlined
in DeNiro (1985) (Table 1). All collagen
samples, including humans and animals,
exhibit C:N ratios of between 3.2 and
3.4, %C values of between 19.2% and
43.6%, and %N values of between 6.9%
and 15.7%. Some of these carbon and nitrogen concentrations are lower than the
ranges for modern collagen, but these
samples nevertheless exhibit acceptable
Isotopic paleodiet analysis at 2nd c AD Rogowo, PL
C:N ratios, and their stable isotope signatures are not anomalous.
The use of FTIR to detect diagenesis is currently limited because there
is no consensus as to acceptable cutoff
points. We report FTIR results to contribute to a growing body of literature
in this area and compare them to previous studies, while recognizing that
FTIR does not provide the same kind
of assurance of sample “quality” as do
collagen quality indicators. FTIR results
of the present study (Table 1) suggest
that carbonate from Rogowo is reasonably well-preserved and likely retains
biogenic δ13Cap signatures. CI values
range from 2.7 to 4.2 (mean=3.6±0.4)
and C/P ratios range from 0.10 to 0.41
(mean 0.18±0.07). These values resemble ranges of acetic-treated archaeological carbonate estimated to be well-preserved elsewhere (e.g., Katzenberg et al.
2009). For comparison, modern bones
treated with acetic acid to mimic archaeological sample preparation exhibit CI
values of between 2.7 and 3.6 (Niel­senMarsh and Hedges 2000b; Wright and
Schwarcz 1996). Shemesh (1990) advocates considering 3.8 a maximum value
for archaeological, acid-treated samples,
above which samples should no longer
be considered well-preserved. This is
relatively conservative, as de la Cruz Baltazar (2001) reports a CI range of 2.8–4.0
in a well-preserved archaeological sample, Katzenberg et al. (2009) consider
a cut-off of 4.0, and Wright and Schwarcz
(1996) report well-preserved values
above 4.0. In terms of C/P, modern bones
treated with acetic acid exhibit values of
0.10–0.24 (Wright and Schwarcz 1996).
Acetic-treated archaeological C/P values
tend to be slightly lower (c.f., Katzenberg
et al. 2009). Although several samples
from 2nd c. Rogowo exhibit higher CI and
7
lower C/P than modern bones, there is
no relationship between either FTIR CI
or C/P and either δ18O or δ13C, which has
been used elsewhere as a guideline for
identifying diagenetically altered samples (c.f., Garvie-Lok 2001) (Fig. 3). Ten
of the apatite samples exhibit distinct
peaks at wavenumber 1096 cm–1 indicating francolite in the apatite matrix, meaning they are more likely than other samples to have been diagenetically altered
(c.f., Katzenberg et al. 2009; Wright and
Schwarcz 1996). Nevertheless, throughout the sample, peaks are not consistently associated with anomalous CI, C/P
or stable isotope ratios (Fig. 3). In keeping with the recommendations of previous researchers (Garvie-Lok 2001; Nielsen-Marsh and Hedges 2003a; Wright and
Schwarcz 1996), rather than considering
FTIR indices as isolated and finite exclusion criteria, we consider them alongside
other indicators of diagenetic alteration,
including correlations between the the
FTIR data and stable isotope values. In
the following discussion we report statistical results of the overall apatite sample
(n=29) as well as a more conservative
restricted sample (n=13; values italicized in Table 1) comprising only those
individuals with CI values of 3.6 or lower, and CI values between 0.15 and 0.70
(Berna et al. 2004; Szostek et al. 2011).
In addition to medieval Polish fauna,
Roman era faunal data from Denmark are
included for comparison to the human
values from Rogowo in the absence of
directly asssociated animal bones (Table
2). Jørkov et al. (2010) report that 3 cows
exhibit a mean δ13C of –21.6±0.7‰ and
a mean δ15N of 5.7±0.5‰, and 4 pigs
exhibit a mean δ13C of –22.1±0.8‰ and
a mean δ15N of 8.6±0.9‰.
Stable isotope data for humans are
presented in Table 1. Rogowo ­
δ13Ccoll
8
Laurie J. Reitsema and Tomasz Kozłowski
Fig. 3. Indicators of bone mineral diagenesis considered in the present study include (1) the crystallinity
index (FTIR CI), (2) carbonate content in bone, estimated through Fourier transform infrared spectroscopy (FTIR C/P), (3) the presence of a peak at FTIR wavelength 1096 cm–1, and (4) any relationship
between FTIR indices and stable carbon (δ13C) or oxygen isotope (δ18O) values from apatite. FTIR CI
and C/P are correlated, as expected for bone apatite. Although some absolute FTIR indices are questionable, the fact that no correlations exist among FTIR and stable isotope values suggests the samples
may be reasonably well-preserved
values range widely from –19.5‰ to
–16.4‰ (mean=–17.9±0.7‰) and
δ15N values range from 8.6‰ to 10.9‰
(mean=9.7±0.5‰) (Fig. 4). There is
no correlation between δ13Ccoll and δ15N
values (R2 =0.1463), which could occur
when 13C-enriched fish (marine or anadromous) are a major source of protein in
the diet (e.g., Ambrose et al. 1997). δ13Cap
values range from –13.09‰ to –9.69‰
Sex
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
ID
59*
25*
780*
29*
51*
705
100
708
752
56
688N
45
104
38
23
680
774
615
694
428
699
339
440
676
743
39
767
43
48
438
%N
22–35
6.9
22–35
13.3
22–35
13.5
22–35
14.4
22–35
14.5
35–55
8.5
35–>60
9.5
35–55
9.6
22–35
10.1
22–55
10.3
22–35
12.7
22–35
13.1
22–35
13.7
35–55
13.8
22–35
14.2
22–35
7.9
35–55
8.0
20–35
9.6
>55–60
11.9
22–35
12.0
20–35
12.3
22–35
12.3
35–55
12.5
35–55
12.8
20–35
12.8
35–55
12.9
20–35
13.1
22–35
13.2
35–55
14.0
22–35
14.2
Mean ± sd: 11.9±2.2
Age
19.2
36.9
38.0
39.9
40.1
23.3
26.4
26.3
27.9
28.1
35.0
37.2
37.3
38.7
39.3
22.0
22.1
26.6
32.8
34.3
33.8
35.6
35.6
35.1
35.5
36.4
35.8
36.1
38.9
39.2
33.1±6.1
%C
3.2
3.2
3.3
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.3
3.2
3.3
3.2
3.2
3.2
3.2
3.2
3.3
3.2
3.4
3.3
3.2
3.2
3.3
3.2
3.2
3.2
3.2
3.2±0.05
C:N
9.2
9.4
9.6
10.7
9.7
9.3
9.8
8.6
9.9
9.4
9.0
9.3
9.5
9.7±0.01
10.0
9.7
9.9
9.7
9.3
10.1
9.9
10.1
9.9
10.3
10.9
9.9±0.01
8.9
10.4
8.9
9.3±0.04
9.7±0.5
δ15NAir (‰)
–16.8
–17.5
–18.1
–17.5
–18.2
–16.9
–18.5
–18.0
–17.7
–16.9
–16.4
–17.2
–17.0
–18.2±0.03
–17.9
–19.1
–18.2
–19.0
–17.9
–17.7
–18.9
–17.4
–17.4
–19.5
–18.3
–17.7±0.15
–17.3
–18.8
–18.5
–17.9±0.02
–17.9±0.7
δ13Ccoll (‰)
CI
C/P
–10.95
3.4
0.24
–9.69
3.4
0.26
–
–
–
–11.26±0.14
3.8
0.16
–11.46
4.1
0.13
–11.01
4.2
0.13
–12.49
3.8
0.15
–11.51
3.1
0.20
–12.06
2.7
0.41
–11.61
3.4
0.19
–10.46±0.01
3.9
0.15
–11.73
3.9
0.14
–11.32
3.5
0.18
–11.27
4.1
0.15
–10.74
3.3
0.33
–12.17±0.03
2.9
0.29
–11.98
3.9
0.15
–13.07
3.5
0.18
–11.94
3.8
0.16
–11.96
4.2
0.14
–13.09
3.0
0.19
–10.40
4.0
0.17
–12.18
4.0
0.14
–11.39
3.8
0.10
–12.31
2.9
0.24
–11.32
3.8
0.15
–11.20
3.1
0.20
–12.14
3.8
0.14
–12.11
4.2
0.14
–11.55
3.6
0.15
-11.60 ± 0.76 3.6 ± 0.4 0.18 ±0.07
δ13Cap (‰)
Peak
Smooth
–––
Smooth
Shoulder
Peak
Smooth
Peak
Shoulder
Smooth
Shoulder
Shoulder
Peak
Peak
Smooth
Smooth
Shoulder
Peak
Smooth
Peak
Peak
Shoulder
Smooth
Smooth
Peak
Smooth
Shoulder
Smooth
Peak
Smooth
1096cm–1
Table 1. Collagen quality indicators, stable isotope values, and Fourier transform infrared spectroscopy (FTIR) results from all humans. Values appearing in italics exhibit FTIR indices these are given special consideration in the text, and excluded from some analyses
Isotopic paleodiet analysis at 2nd c AD Rogowo, PL
9
Laurie J. Reitsema and Tomasz Kozłowski
10
Table 2. Comparative faunal baseline
3.2
δ15NAir
(‰)
7.8
δ13Ccoll
(‰)
–20.7
δ13Cap
(‰)
–11.41
Present study
38.0
3.3
7.9
–21.0
–
Present study
13.1
36.7
3.3
7.6
–21.5
–
Present study
Cow Bos primigenius
taurus
15.7
43.6
3.2
6.4
–21.0
–
Present study
810-02 Cow Bos primigenius
taurus
14.4
40.2
3.2
6.4
–21.3
–13.80
Present study
ID
%N
%C
C:N
816-02 Cow Bos primigenius
taurus
14.6
40.4
834-02 Cow Bos primigenius
taurus
13.4
839-02 Cow Bos primigenius
taurus
200
Species
Reference
100
Pig Sus scrofa
domesticus
16.1
44.5
3.2
7.9
–21.6
–14.89
Present study
119-05
Pig Sus scrofa
domesticus
12.9
35.6
3.2
5.9
–21.6
–14.71
Present study
816-02
Pig Sus scrofa
domesticus
13.2
37.6
3.3
6.8
–19.8
–12.66
Present study
8.6±0.9
–22.1±0.8
Jørkov et al.
(2010)
5.7±0.5
–21.6±0.7
Jørkov et al.
(2010)
Pig Sus scrofa
domesticus (n=4)
Cow Bos primigenius
taurus (n=7)
(mean=–11.60±0.76‰). When only
apatite samples with FTIR CI values
of 3.6 or lower and C/P values of between 0.15 and 0.70 are considered
Fig. 4. Stable carbon (δ13Ccoll) and nitrogen (δ15N) isotope data from collagen from Rogowo, including 15
males, 5 females buried with jewelry, and 10 females buried without jewelry
Isotopic paleodiet analysis at 2nd c AD Rogowo, PL
11
Fig. 5. Stable carbon isotope data from carbonate (δ13Cap) and collagen (δ13Ccoll) from Rogowo (n=29)
(n=13), the mean δ13Cap value is similar
(–11.64±0.93). δ13Ccoll and δ13Cap values
are modestly positively correlated at Rogowo (R2=0.3439) (Fig. 5). When the
restricted δ13Cap sample of just 13 individuals is used, δ13Ccoll and δ13Cap values
remain modestly positively correlated
(R2=0.4482). Δ13C(ap-coll) values range
from 5.3‰ to 8.1‰ (mean=6.3±0.7‰).
The δ13C values of men and women are significantly different: both the
­δ13Ccoll and δ13Cap values of females are
higher (Kruskal-Wallis Test, p=0.014
and p=0.015, respectively). When only
apatite samples with FTIR CI values of
3.6 and are considered (n=13, 7 females
and 6 males) this δ13Cap difference remains (Kruskal-Wallis Test, p=0.032).
Women exhibit lower mean δ15N than
m­en (Kruskal-Wallis Test, p=0.078).
Five female skeletons buried with jewelry were analyzed. The δ13Ccoll, δ13Cap and
δ15N values of women with and without
jewelry are similar, although δ13Cap of
women without jewelry is generally low-
er, albeit not significantly so (all 15 females, p=0.157; 7 females with CI ≤3.6,
p=0.121). The richest grave at Rogowo
is skeleton R–59-F, a woman buried with
substantial quantities of jewelry (Fig. 2),
which we consider in more detail on account of her unusual mortuary context.
This individual exhibits relatively high
δ13Ccoll value (–16.8‰) compared to
mean values, but the value is similar to
several other females (R-705-F, R-56-F,
R-688N-F, R-104-F). Furthermore, her
δ13Cap (–10.95‰), Δ13C(ap-coll) (5.9‰), and
δ15N values (9.3‰) are unremarkable.
Discussion
Diet Reconstruction
δ15N values suggest a predominantly terrestrial diet at Rogowo. δ13C values indicate a mixed diet of C3 plants, C4 plants,
and fish. If a diet-collagen spacing relationship of +5‰ is assumed, the pro-
12
Laurie J. Reitsema and Tomasz Kozłowski
tein diet of individuals at Rogowo can be
inferred to have a δ13C value of –21.4‰
to –24.5‰. In agreement with this, if
a +12‰ diet-carbonate fractionation
factor is applied (c.f., Garvie-Lok 2001:
125–128; Prowse et al. 2005), the δ13C
values of bulk diets at Rogowo ranged
between –21.7‰ and –25.0‰. The expected isotopic “space” of a C3 diet is at
the lower end of this range, –23.0‰ to
–25.0‰ (Garvie-Lok 2001). Thus, C3
foods appear to have dominated diet at
Rogowo, but foods with a higher δ13C
signature also contributed to both the
energy and protein sources of the diet
(namely, millet and marine and/or anadromous fish).
A C4 signal could have contributed
to diet in two ways: through direct consumption of millet by humans, or indirectly through consumption of animals
foddered on millet. Sampling local animals is the most straightforward way to
resolve this, but it is also possible to explore whether C4-foddered animals contributed to human diet by checking for
a correlation between δ13C and δ15N values. A closer look at Figure 4 shows that
individuals with δ13C values of greater
than –18.0‰ exhibited the entire range
of δ15N values. The fact that δ13C and δ15N
values are not positively correlated at Rogowo (R2 =0.1463) supports an interpretation of direct millet consumption, rather than C4-foddered animal consumption.
The δ13Cca values from Rogowo suggest
millet contributed between 0% and 35%
to overall diet, depending on the individual. This corroborates archaeobotanical evidence for a broad-spectrum agricultural
strategy including millet, barley, rye, oats
and wheat (Wasylikowa et al. 1991).
The lack of a correlation between δ13C
and δ15N values would seem to caution
against an interpretation of marine or
anadromous fish consumption. δ13C and
δ15N values from both marine and anadromous fish bones tend to be higher
than those of terrestrial animals, and
humans eating such fish exhibit a correlation between the two isotopes (e.g.,
Ambrose et al. 1997). However, a growing number of studies reveal that stable
isotope ratios of fish bones are highly
variable (c.f., Dürrwächter et al. 2006;
Fuller et al. 2012; Katzenberg et al. 2009;
Müldner and Richards 2005; Redfern et
al. 2010; Reitsema et al. 2013). Consequently, a straightforward correlation
between δ13C and δ15N among fish-eating
humans may not always exist.
To further explore the issue of fish
in diet, we consider Rogowo in relation
to other European samples. In Figure 6,
collagen data from Rogowo (mean±1σ)
are shown alongside 9 previously reported European historical populations. Four
of these are reported to have consumed
a predominantly or exclusively terrestrial
diet with only C3 foods: a 4th c. AD Late
Roman sample from England (Richards
et al. 1998), a 5th–2nd c. BC Greek colonial sample from Bulgaria (Keenleyside et
al. 2006), a 2nd c. sample from England
(Chenery et al. 2010), and a 1st–4th c. AD
Roman Iron Age sample from Denmark
(Jørkov et al. 2010). Three comparative
samples consumed predominantly or
exclusively terrestrial diets that also included C4 foods: several Hallstatt groups
from Austria (Le Huray and Schutkowski
2005), a 9th–5th c. Iron Age sample from
Slovenia (Murray and Schoeninger
1988) and an 11th–12th c. AD early medieval population from Poland (Reitsema et al. 2010). Finally, two comparative
samples reportedly consumed marine
foods in addition to C3 terrestrial foods:
2nd–5th c. skeletons from Roman Tunisia
(­Keenleyside et al. 2009) and a Roman
Isotopic paleodiet analysis at 2nd c AD Rogowo, PL
era sample from Sweden (Eriksson et al.
2008).
δ15N values place Rogowo near other
populations with terrestrial diets. Although the δ15N values at Rogowo are
not the highest among the terrestrial
diets displayed in Figure 6, cautioning
against an interpretation of a high-fish
diet, they are high in comparison to the
lower cluster of populations. For example, the mean δ15N value from another
Polish sample dating to the 11th–12th c.
is 9.2±0.6‰ (approximately 3‰ higher than its faunal baseline) (Reitsema
et al. 2010). δ15N values at Rogowo
(9.7±0.5‰) are higher than the Giecz
sample. Interestingly, humans’ δ15N values at Rogowo are still just 2.5‰ higher than domestic animal values reported
by Reitsema et al. (2013) from nearby
Kałdus, a medieval settlement approximately 1000 years younger than Rogowo. A diet-tissue difference of 2.5‰
is a reasonable expectation for consumers of terrestrial animal protein. As previously discussed, the medieval animals
from Kałdus exhibit unusually high δ15N
values likely due to land management
practices (e.g., manuring, ploughing,
fire-clearing, etc.). At some point in antiquity, the local baseline δ15N in this region of Poland may have been raised by
human land management strategies such
as burning or fertilizing fields (Bogaard
et al. 2007; Commisso and Nelson 2008;
Grogan et al. 2000), and it is possible
this occurred as early as the Roman era.
A grain of wheat sampled from a nearby
modern field yielded a high δ15N value of
7.2‰, which could be due to the influence of either modern or past land management strategies on soil nitrogen (c.f.,
Commisso and Nelson 2008). Compared
to the Roman era animals from Denmark
reported by Jørkov et al. (2010) which in
13
general exhibit lower stable isotope values, humans’ δ15N values at Rogowo are
4‰ higher than cows and 2‰ higher
than pigs. Accepting either the Polish or
the Danish faunal baseline would still indicate a predominantly terrestrial diet, if
a diet-tissue spacing of 3–5‰ is accepted
for δ15N (Drucker and Bocherens 2004).
In terms of δ13C values in Figure 6,
Rogowo overlaps with Hallstatt populations in Austria that consumed a C4
plant, millet. However, C3 plants still
predominated in the diet: Rogowo δ13Ccoll
values are considerably lower than those
of a Slovenian population that consumed
large amounts of millet (or millet-foddered animals). Millet has also been detected isotopically in human remains in
early medieval Poland (Reitsema 2012;
Reitsema et al. 2010), Bronze Age Italy (Tafuri et al. 2009), Iron Age Austria
and Slovenia (Le Huray and Schutkowski
2005; Murray and Schoeninger 1988),
and possibly as early as the Neolithic in
Poland (Kozłowski et al. 2013). Unlike in
Eastern and Southern Europe, millet is
not widespread in Western Europe. With
its occurrence following cultural distribution patterns rather than geography
or climate, millet appears to characterize
diets of Slavic populations. In her book
documenting the history of Polish cuisine, Maria Dembińska posits that “…
the Polish preference for millet was cultural and that millet must have arrived
with the earliest Slavic migrants” (104).
That millet might be used as a proxy for
Slavic migrations is an interesting possibility, given the controversy surrounding
the relationship between the Wielbark
culture and the issue of Slavic ethnogenesis (c.f., Dąbrowski 2006). Millet
consumption among Wielbark and early
medieval Polish populations represents
a potentially significant continuity be-
14
Laurie J. Reitsema and Tomasz Kozłowski
Fig. 6. Collagen stable isotope data (carbon: δ13Ccoll; nitrogen: δ15N) from Rogowo (n=30) compared to
other European populations
tween the Roman era and the medieval
period in Poland.
A model for using both δ13C from carbonate and collagen was developed by
Kellner and Schoeninger (2007) to provide a clearer idea of protein and energy in diet. The model consists of three
regression lines that were derived from
controlled feeding experiments with animals. Each line represents a particular
diet: one based on C3 protein, one based
on marine protein, and one based on C4
protein. The end points of each line represent either 100% C3 energy (bottom) or
100% C4 energy (top). Using this model,
it is possible to tease apart sources of stable isotope variation from small amounts
of fish or millet. In Figure 7, both types
of δ13C data from Rogowo are displayed
in comparison to several other Europe-
an populations after shifting the regression lines by +1.5‰ for both δ13Ccoll and
δ13Cap to account for the Suess effect, by
which the modern-day atmospheric δ13C
value is lower than in the past due to recent fossil fuel emissions (Marino and
McElroy 1991). All 29 apatite samples
are included but the 16 samples whose
FTIR CI values exceed 3.6 and C/P values are below 0.15 are demarcated with
an “X”. The importance of millet in diet
is supported by Rogowo’s location at the
middle of the C3 protein line, rather than
towards the base where “C3-only” populations would plot. The fact that Rogowo
plots to the right of the C3 protein line
indicates that dietary protein came from
primarily C3 terrestrial fauna, but with
supplemental input from marine or anadromous fish.
Isotopic paleodiet analysis at 2nd c AD Rogowo, PL
Few comparative populations are
available for use in Figure 7 because collagen and carbonate are not yet commonly analyzed together in stable isotope
studies of Europe. Pictured are: six populations from Neolithic Greece including
three from coastal areas and three from
further inland (Papathanasiou 2003),
a medieval Polish population (Reitsema
et al. 2010), Roman populations from
Tunisia (Keenleyside et al. 2009) and Italy (Prowse et al. 2005), and humans from
Viking era and medieval Sweden (­Kosiba
et al. 2007). Populations consuming fish
plot to the right of the C3 protein line in
this figure with one exception: the Roman Italian sample from Prowse et al.
(2005) reportedly consumed some marine foods, but plots left of the C3 pro-
15
tein line. Also to the left of the line are
populations from inland Greece where
marine foods were negligible. Rogowo
appears very similar to Roman era Tunisia, where fish made significant contributions to diet (Keenleyside et al. 2009).
Interestingly, the δ15N values from Rogowo are considerably lower than those
from the Tunisian sample (9.7±0.5‰ vs.
12.8±1.3‰). We conclude that anadromous or marine fish were consumed in
supplemental amounts at Rogowo, and
that they probably had relatively low δ15N
values. A “fish signal” thus emerges only
when using the model from Kellner and
Schoeninger (2007), and is not apparent
when examining collagen data alone.
The nearby Vistula River, along with its
tributaries and oxbow lakes, would have
Fig. 7. Stable carbon isotope data from carbonate (δ13Cap) and collagen (δ13Ccoll) from Rogowo (n=29)
compared to other European populations. Regression lines are from Kellner and Schoeninger (2007).
Because the regression lines were developed using modern animal bones, which will exhibit systematically lower δ13C values due to differences between modern and pre-industrial atmospheric CO2 values
stemming from fossil fuel emissions (Marino and McElroy 1991), regression lines are shifted to be
1.5‰ higher to make them comparable with the archaeological human samples. Sixteen samples exhibiting crystallinity indices (FTIR CI) in excess of 3.6, and carbonate content (FTIR C/P) below 0.15
are demarcated with a white “X” through the data symbol
16
Laurie J. Reitsema and Tomasz Kozłowski
provided the population at Rogowo with
freshwater (carp, bream, roach) and anadromous (sturgeon) fish. Oxbow lakes
composed of shallow, still water were
also present in the region which may
contain fish with very low δ15N values
and relatively high δ13C values (Hecky
and Hesslein 1995). Three anadromous
fish (sturgeon) from another nearby medieval settlement, Kałdus, show δ13C values of –15.6‰ to –17.1‰ and of 9.9‰
to 11.3‰ (Reitsema et al. 2013). Consumption of these fish would be fairly
consistent with the human stable isotope
data we have reported. However, their
contribution to diet was probably supplemental. Other sotopic paleodietary
research has demonstrated that European populations in the first centuries AD
were not exploiting aquatic resources
though they presumably had the means
(e.g., Chenery et al. 2010; Jørkov et al.
2010; Richards et al. 1998). Like these
other populations, the subsistence economy at Rogowo was based on animal
husbandry and agriculture.
Intrapopulation Variation
Sex-based differences in stable isotope
ratios at Rogowo suggest that diets of
women included more millet, and possibly less animal protein (meat or dairy)
than diets of men. Sex-based social differentiation is a characteristic of many
tribal societies and at Rogowo, appears
to have translated into differential food
consumption. Sex-based differences in
diet from this time period are reported
by other stable isotope and trace element
studies from this time period in Europe
(e.g., Fuller et al. 2006; Redfern et al.
2010; Richards et al. 1998; Smrćka et al.
2000). However, such differences do not
necessarily implicate sex-based inequali-
ties among the population. Women and
men may have performed different subsistence tasks throughout the day, simply
exposing women and men to different
foods. Increased consumption of plants
in general would augment a “millet signal” in bones of women at Rogowo, because it would no longer be so strongly
masked the available C3 protein from terrestrial animals.
It is also possible that the δ13C differences between men and women are
non-dietary. Plants from warm climates
have been shown to exhibit higher δ13C
values than the same plants in colder
climates due to temperature-dependent
fractionation of CO2 (van Klinken et al.
2000). Richards et al. (1998) identified
possible immigrants at the Poundbury
site in England based on the individuals’ elevated δ13C values. Perhaps some
women with higher δ13C values migrated
to Rogowo from a warmer climate. Using morphometrics, Gładykowska-Rzeczycka et al. (1997) report that females
buried in another Wielbark cemetery in
Pruszcz Gdański were an “autochthonic
population of Balts” whereas males had
“traces characteristic for Goths-German
tribes that [moved into] the East Pomerania region” (Gladykowska-Rzeczycka et
al. 1997:92), suggesting sex-biased residency patterns. However, contra the evidence from Pruszcz Gdański, if migration
underlies the stable isotope differences
in the present study it would suggest
women were the immigrants at Rogowo.
Analyses of strontium and oxygen isotope values of tooth enamel and bone
from Rogowo are intended to further explore questions of mobility.
Stable isotope differences were not
associated with differences in grave
goods (jewelry) in women’s burials (Fig.
4). This accords with an interpretation of
Isotopic paleodiet analysis at 2nd c AD Rogowo, PL
Wielbark populations as relatively egalitarian, with biological variables (e.g.,
sex) playing a more influential role in
structuring diet than cultural variables
(e.g., status).
Conclusion
Diet at Rogowo was based on terrestrial
foods (meat, milk, and plants), but with
supplemental input from fish (likely lowδ15N anadromous or littoral fish), indicating an overall broad-spectrum subsistence economy. Millet was consumed
at Rogowo, and in greater amounts than
during the medieval period to follow
(c.f., Fig. 6; Reitsema et al. 2010; Reitsema 2012). Stable isotope differences
between the sexes indicate that men and
women may have consumed different
foods, although there is a possibility that
women migrated to Rogowo from an isotopically different region of Europe. No
significant differences are noted in δ13C
or δ15N of burials with and without jewelry, suggesting low status-based social
differentiation among the Wielbark culture, at least in terms of daily food access.
A significant obstacle to paleodiet
studies in Europe using stable isotope
evidence is that most foods are isotopically indistinguishable. Consumption
of the same foods is not necessarily implicated when individuals exhibit similar stable isotope signatures. In some
Eastern and Southern European regions,
millet creates isotopic heterogeneity that
may highlight differential access within
the population. This is the case at Rogowo, but not in Western Europe where
agriculture was entirely based on isotopically homogeneous C3 plants. A second
problem with diet reconstruction in Europe is that stable isotope ratios of fish
17
and terrestrial animals are not always
discrete. The stable isotope ratios of fish
and terrestrial foods frequently overlap,
rendering fish isotopically invisible in
human diet. Even more complications
arise when past land management strategies such as manuring, ploughing and
burning fields raise δ15N values at the
base of the human food web, or when
human consumption of legumes such
as peas lowers δ15N values. Because of
these obstacles it is helpful to consider
relationships between different stable
isotope ratios (δ15N, and δ13C from both
collagen and apatite) and other patterns
in the data, rather than simply comparing stable isotope ratios obtained from
human bones to expected ranges. Considerations such as these have permitted the identification of millet and anadromous or marine fish consumption at
Rogowo. Stable carbon and nitrogen isotope data accord with paleobotanical and
archaeozoological evidence for a mixed
subsistence economy of agriculture and
animal husbandry, and contribute new
information regarding the roles of biology and culture in structuring diet and
possibly social structure of the relatively
unknown Wielbark culture.
Author contribution
LJR prepared and analysed bone samples
isotopically, obtained grant sponsorship,
and wrote the manuscript; TK contributed bone material for the study, provided
archaeological and contextual information about the site, and edited drafts of
the manuscript.
Conflict of interests
The authors declare that there is no conflict of interests.
18
Laurie J. Reitsema and Tomasz Kozłowski
Acknowledgments
We thank Andréa Grottoli and Yohei
Matsui at The Ohio State University Stable Isotope Biogeochemistry Laboratory,
Rachel Kopec and Stephen Schwartz at
The Ohio State University Department
of Food Sciences and Technology, Daniel
Makowiecki at the Nicolaus Copernicus
University, and Douglas E. Crews at The
Ohio State University Human Biology
Laboratory.
Corresponding author
Laurie J. Reitsema, Department of Anthropology, University of Georgia, 250
Baldwin Hall, Jackson St., Athens Georgia 30602, USA
e-mail address: reitsema@uga.edu
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